Why Agents Need a Passport: .fafa — Portable Identity for the Agentic Era

Abstract

This paper specifies .fafa (application/vnd.fafa+yaml), the IANA-registered media type for declarative agent identity: a portable passport for who an agent is, what it may do, where it is reached, and what it must never do. It complements Agent Cards, Model Context Protocol server-cards, and AGENTS.md; it does not replace them. In production, that identity is usually inferred from system prompts, product settings, and protocol-native cards that do not travel cleanly across hosts — seam rewrites, inference cost, and trust surfaces that cannot be diffed. A .fafa document is simple, structured, and persistent. Its lifecycle is author → serve → discover → project. House cards stay the wire format; AGENTS.md stays the repo ops briefing; .fafa answers who the agent is. The paper is self-contained. Multi-agent orchestration, deep composition, and scoring are deferred.